Project Summary Levels and growth of health care spending in the United States are among the highest in the developed world, leading to increased urgency by policymakers and payers to find ways to control spending. One popular strategy is through consumer-focused changes in insurance benefit design, which alter consumer exposure to prices and the relative value of services they seek. There is substantial variation in the structure of these benefit design changes, so while there is a robust literature around optimal insurance design, the number of structures and potential settings in which they may be applied have left key questions unanswered. In particular, it is not well understood how consumers? exposure to service price impacts the efficiency of health service utilization and the use of strategies to make health care more affordable. The proposed dissertation uses quantitative methods to examine the effects on efficiency and affordability in two popular types of insurance benefit structures: high-deductible health plans (HDHPs), which raise front-end cost sharing through higher deductibles, and value-based insurance design (V-BID) plans, which alter the cost sharing structure by removing financial barriers for services that are clinically valuable. In line with intended policy goals, each of these plans have been shown to improve some measures of efficiency: HDHPs lower health care spending and V-BID plans improve use of high-value health care services. Yet, there are key gaps in knowledge about the full impacts of each benefit structure. Within HDHPs, enrollees would ideally shop among different-priced providers to achieve greater affordability, yet limited evidence suggests this is not the case. Large studies of consumer behavior have not been done to confirm this finding and, crucially, there is very little understanding of why HDHP enrollees appear reluctant to shop. I use one of the largest datasets of administrative claims available to examine whether HDHP enrollees pay lower prices relative to when they were in traditional plans. Further, I assess whether the structure of the market in which enrollees receive care affects their price shopping behavior in HDHPs. Within V-BID plans, a key efficiency question is whether precisely targeted changes in consumer cost-sharing structures translate into precise utilization patterns. That question has been answered in part; targeted services are affected by V-BID implementation. I focus on whether there are spillover effects in the form of unintentional changes in the utilization of non-targeted services. These spillover effects may attenuate the ability of V-BID plans to encourage efficient medical care. My research focuses on better understanding how benefit design contributes to the efficiency and affordability of health care ? a goal consistent with the mission of AHRQ. Results from this study will inform organizational and public policy as to how structural changes in benefit design affect overall spending and consumer welfare.